Broad band phase measuring system for microwave pulses

ABSTRACT

Microwave pulse phase-measuring apparatus having a pump or local oscillator feeding a pair of up-converters or mixers in a heterodyne conversion technique, the pump or local oscillator output being fed to the up-converters, down converters, or mixers by transmission lines having different effective lengths. The pump or local oscillator is frequency modulated with a voltage ramp initiated by the received signals, thereby causing a continually increasing relative phase shift of the up-converter signals through a point of phase coincidence, the magnitude of the voltage ramp at the instant of phase coincidence being sampled to provide a measurement.

States Pten [72] Inventor Donald L. Margerum Woodland lllills, Calii'.[21] Appl. No. 682,708 22 Filed on. 23, 1967 [45] Patented Oct. 5, 197i[73] Assignee Singer-General Precision, inc.

[54] BROAD BAND PHASE MEASURHNG SYSTEM FOR MlCMOWAVlE PULSES 10 Claims,7 Drawing Figs.

[52] U.S. Cl 324/85, 324/84 [51] lnlLCll G01r25/02 [50] Field of Search324/84, 85

[56] References Cited UNlTED STATES PATENTS 3,248,647 4/l966 EichakerPrimary Examiner-Rodney D. Bennett, Jr. Assistant Examiner-Richard E.Berger I Attorney-Thomas W. Kennedy ABSTRAKIT: Microwave pulsephase-measuring apparatus having a pump or local oscillator feeding apair of up-converters or mixers in a heterodyne conversion technique.the pump or local oscillator output being fed to the up-converters, downconverters, or mixers by transmission lines having different effectivelengths. The pump or local oscillator is frequency modulated with avoltage ramp initiated by the received signals, thereby causing acontinually increasing relative phase shift of the up-converter signalsthrough a point of phase coincidence, the magnitude of the voltage rampat the instant of phase coincidence being sampled to provide ameasurement Plums Mensa/fly Grim/@ 5 Phase ,Uezcfan PATENTEUUET BIB?!361L135 SHEEY 1 OF 3 PATENTEUBBT 1% 3611135 SHEU 2 [1F 3 BROAD BANDPHASE MEASURING SYSTEM FOR MICROWAVE PULSES The rapid detection andmeasurement of phase differences between electrical signals at microwavefrequencies has important application in the electronic art, such as indirection finding and frequency measuring devices, for example. Incertain applications it is desirable to rapidly measure phasedifferences between a succession of unrelated short signal pulses, suchas radar pulses, occurring over a wide range of frequencies, with themeasurement being substantially independent of signal strength. Theability to make such measurements on each arriving wave pulse isimportant in many electronic reconnaissance systems.

Although the use of interferometers to determine angle of arrival hasbeen long well known in the art, it has been only relatively recentlythat phase-measuring equipment was developed which is capable ofmeasuring angle of arrival during a submicrosecond pulse of incidentenergy. Prior art interferometer systems for single pulse responsetypically utilize closed loop electronic servos or tapped line standingwave indicators. The closed loop servo technique is limited in speed ofresponse to about l microsecond and limited in bandwidth to a practicalvalue of one octave or less, the system bandwidth being determined bythe bandwidth of the electronically controlled phase shifters employed.The tapped line standing wave indicator is limited in sensitivitybecause of the necessarily loose coupling at each end of the tappedpoints along the transmission lines, and this type of indicator requiresa multiplicity of receivers, one for each tap on the line. Also,degradation of accuracy from internal reflections in the tapped linestanding wave indicator represents a serious limitation on itsusefulness.

It is particularly desirable that certain electronic reconnaissanceapparatus include an ultrabroadband direction finding and frequencymeasuring system having the capability of submicrosecond response toincident radiation over at least a three or four octave band ofmicrowave frequencies, and preferably greater. Due to the bandwidthlimitations of the hereinabove discussed closed loop servo and tappedline standing wave indicator techniques, a multiplicity of systems hasheretofore been necessary in order to achieve operation over a widebandwidth.

The present invention is directed toward an ultrabroadbandphase-measuring system having the capability of responding in as littleas one-fourth microsecond to incident radiation over a wide band ofmicrowave frequencies considerably greater than one octave. By coveringsuch a wide band in one system the size, weight and cost of thenecessary equipment is considerably reduced.

It is therefore an object of the present invention to provide improvedphase-measuring apparatus.

It is also an object of the present invention to provide an improvedsystem for measuring phase differences between signal pulses atmicrowave frequencies.

It is another object of the present invention to provide phase-measuringapparatus having a submicrosecond response time over more than an octavebandwidth.

It is a further object of the present invention to providephase-measuring apparatus wherein the measurements are relativelyindependent of differences in signal strengths between the two signalsbeing compared.

It is a still further object of the present invention to provide animproved microwave direction finding system.

It is also an object of the present invention to provide an improvedmicrowave frequency measuring system.

It is yet another object of the present invention to provide a techniquefor increasing the response bandwidth of microwave phase-measuringapparatus.

It is a still further object of the present invention to provide aphase-measuring system having a more than octave bandwidth at microwavefrequencies, wherein the size, weight and cost of the equipment isconsiderably reduced.

The object of obtaining an extremely wide bandwidth is achieved in thebasic embodiment of the present invention system by up-converting thesignals applied to the two system input terminals to compress more thanone octave to less than one octave at a higher frequency whilepreserving the incident phase relationship of these signals, a localoscillator (pump) being employed in common with a pair of up-converters(mixers) in a heterodyne conversion technique. The pump oscillatoroutput is fed to the up-converters by transmission lines havingdifferent effective lengths so that the relative phases of thetip-converted signals can be shifted by slightly shifting the pumposcillator frequency. The phase difference between the applied inputsignals is determined by frequency modulating the common pump oscillatorby a voltage ramp initiated in response to the applied input signals tothereby cause a continually increasing relative phase shift of theup-converted signals through a point of phase coincidence, the magnitudeof the voltage ramp at the instant of phase coincidence beingproportional to the phase difference between the signals applied to thesystem input terminals.

In the hereinbelow illustrated embodiment of the basic present inventionphase-measuring apparatus the pump is a voltage controlled oscillator,and the output signals of the upconverters are combined in a phasedetector having phase sum and phase difference pulse outputs, Le, afirst output having pulse magnitudes proportional to the sum of thephases of signals applied to its inputs and a second output having pulsemagnitudes proportional to the difference in phase between signalsapplied to its inputs. The phase sum output of the phase detector is fedto a ramp generator to initiate the voltage ramp. The output of the rampgenerator is fed to the voltage controlled oscillator as the controlvoltage therefor, and also to a voltage sampling circuit which istriggered by the phase difference output of the phase detector to samplethe voltage ramp at the instant that phase detector output undergoes aphase reversal (the zero crossing point), and to hold this sampledvoltage, the sampled voltage being proportional to the phase differenceof the signals applied to the system input terminals.

This basic phase-measuring apparatus can be used to mea sure the angleof arrival or the frequency of received signals over a bandwidthconsiderably greater than an octave and can easily be modified to covertwo separate frequency ranges, as will be hereinbelow explained.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof will be better understoodfrom the following description considered in connection with theaccompanying drawing in which a presently preferred embodiment of theinvention is illustrated by way of example. It is to be expresslyunderstood, however, that the drawing is for the purpose of illustrationand description only, and is not intended as a definition of the limitsof the invention. In the drawing:

FIG. 1 is a schematic diagram in partial block form of a preferredembodiment of the present invention phase-measuring system;

FIG. 2 is a schematic diagram, partially in block form, of a colinearinterferometer utilizing the basic system of FIG. ll;

FIG. 3 is a schematic diagram, partially in block form of frequencymeasuring apparatus incorporating the basic system of FIG. 1;

FIG. 4 is a schematic diagram in partial block form of a phase-measuringsystem for two separate frequency ranges;

FIG. 5 is a typical phase plane plot for the interferometer of FIG. 2;

FIG. 6 is a schematic diagram showing typical circuitry of the rampgenerator for FIG. 1; and

FIG. 7 is a schematic diagram showing hold circuitry for FIG. I.

Turning now to FIG. I of the drawing there is shown a block diagram ofthe basic present invention phase-measuring device, the circuit beinggenerally indicated by the reference numeral 10 and enclosed within thedashed line rectangle. The phase-measuring device 10 is provided withtwo signal input typical sample and terminals, designated by thereference numerals 11 and 12, for application to the system of theelectrical signals between which phase differences are to be measured.

Signals applied to the input terminal 1 l are fed to a first upconverterdevice 20 by an electrical lead 13. Signals applied to the inputterminal 12 are fed to a second up-converter device 30 by an electricallead 14. The up-converters 20 and 30 function as mixers in anup-conversion heterodyne system as will be hereinbelow explained. Theup-converters 20 and 30 can be the conventional resistive type ofmicrowave mixer, or can be parametric upconverters.

The RF carrier fed to the up-converters by leads l3 and 14 is commonlyreferred to as the "signal frequency," and the RF from the localoscillator is commonly referred to as the pump frequency. In the presentinvention circuit a voltage controlled oscillator 40 is provided as acommon pump for both of the up-converters 20 and 30, the VCO outputbeing fed to the up-converter 20 by a transmission line 41 and to theup-converter 30 by a transmission line 42, the effective length of thetransmission line 42 being longer than that of the line 41. The VCO 40can be viewed as the local oscillator in the heterodyne system with theup-converters 20 and 30 functioning as mixers.

The outputs of the up-converters 20 and 30 will be at frequencies whichare the sum and difierence of the pump frequency and the signalfrequency. For example, reception of a 2 Ge. (gigacycle or gigal-lertz)signal with a 14 Ge. pump frequency will result in up-converter outputsat 12 and 16 Ge. It is presently preferred to utilize only thedifference frequency output of resistive mixers, so the output of theup-converter 20 is fed through an electrical lead 21 to a low-passfilter 22 having a cutoff frequency slightly higher than the highestdifference frequency to be encountered, in order to filter out the pumpfrequency and the sum frequency output. In a similar manner, the outputof the up-converter 30 is fed through an electrical lead 31 to alow-pass filter 32. In a similar manner, the output of the up-converter30 is fed through an electrical lead 31 to a low-pass filter 32. In atypical system for operation over the 3 to l bandwidth of 2-6 Gc. andwith the VCO 40 operating at 14 Gc., the cutoff frequency of thelow-pass filters 22 and 32 are slightly about 12 Gc. since theup-converter outputs will be within the range of from 8-12 Gc. with thelowest sum frequency output being 14 Ge.

The output of the low-pass filter 22 is fed to an input terminal 51 of ahybrid junction 50 through an electrical lead 16. The output of thelow-pass filter 32 is fed to an input terminal 52 of the hybrid junction50 through an electrical lead 19. The hybrid junction 50 has two outputterminals 53 and 54. The characteristics of the hybrid junction 50 aresuch that upon application of a signal to its input terminal 52 thephase of the signal appearing at the terminal 54 will be lagging 90 withrespect to that of the signal appearing at the terminal 53; similarly,upon application of a signal to its input terminal 51 the phase of thesignal appearing at the terminal 53 will be lagging 90 with respect tothat appearing at the terminal 54, thereby providing a combination inphase quadrature of signals applied to the hybrid junction inputterminals 51 and 52.

Hybrid junctions are well known in the art and hence will not bediscussed in detail beyond stating that in the hybrid junction 50 thereis no direct intercoupling of the input terminals 51 and 52, therebyallowing the isolation of these input terminals from each other whilecoupling signals from both of its input terminals to each of its outputterminals. Hence, input signals are independently vectorially combinedin phase quadrature at the outputs of the hybrid junction 50 with nosignificant interaction between signals applied to its two inputterminals 51 and 52.

One hybrid output is fed from the output terminal 53 to the anodeterminal of a diode video detector 61 through an electrical lead 56. Theother hybrid output is fed from the output terminal 54 to the anodeterminal of a diode video detector63 through an electrical lead 57. Forefficient operation at microwave frequencies the electrical leads 13,l4, 16, 19, 21, 31, 56 and 57 are preferably sections of waveguides orcoaxial cables, although shorter lengths may be stripline.

The cathode terminal of the diode 61 is connected to one input of asumming amplifier 70 and to one input of a difference amplifier 80. Thecathode terminal of the diode 63 is connected to another input of thesumming amplifier 70 and to another input of the difference amplifier80. The summing amplifier 70 is provided with an output terminal 71, thesumming amplifier being provided with an output terminal 81.

The signals appearing at the summing amplifier output terminal 71 willbe pulses having their magnitudes determined by the sum of themagnitudes of the signals appearing at the hybrid output terminals 53and 54, which in turn represent the vector sums of the signals appliedto the hybrid input tenninals 51 and 52 added in phase quadrature, i.e.,E =E +jE and E =E +jE the signals appearing at the difference amplifieroutput terminal 81 being pulses having their magnitude determined by thedifference in the magnitudes of the signals appearing at the hybridjunction output terminals 53 and 54. Thus, it can be seen that thehybrid junction 50, the diodes 61 and 63, the summing amplifier 70 andthe difference amplifier 80 effectively form a phase detector having sumand difference outputs with the difference output yielding zero outputfor in-phase signals applied to terminals 51 and 52 and yielding anincreasing output for small increases of phase shift and a decreasingoutput for small decreases of phase shift between the signals applied to51 and 52, this phase detector being generally indicated by thereference numeral 60 and enclosed within a dashed line rectange. Ofcourse, other suitable embodiments of such a phase detector will beapparent to those skilled in the art.

Output terminal 71 of the summing amplifier 70 (the sum output of phasedetector 60) is fed through a threshold detector 74 to a flip-flop 77,the output of the flip-flop 77 being fed through an electrical lead 78to an input terminal 91 of a ramp generator 90. The ramp generatorfunctions to generate a voltage ramp pulse when triggered by a voltagepulse applied to its input terminal 91. The term voltage ramp pulse" asused herein refers to a triangular pulse having a steep trailing edge soas to form a pulse substantially in the shape of a right triangle, asindicated in FIG. I by the exemplary waveshape appearing above the rampgenerator 90. The voltage ramp pulse output of the ramp generator 90 isapplied through an electrical lead 93 to the VCO 40 as the controlvoltage therefor. The VCO 40 is a microwave oscillator the outputfrequency of which can be varied in response to an applied controlvoltage, a klystron type of oscillator being presently preferred.

Output terminal 81 of the difference amplifier 80 (the difference outputof phase detector 60) is fed through a differentiator 84 to a flip-flop87, the output of flip-flop 87 being fed through an electrical lead 88to one input of sample and hold circuitry generally indicated by thereference numeral 95, the output of the ramp generator 90 also being fedto another input of the sample and hold circuitry through an electricallead 96.

The sample and hold circuitry 95 is arranged to be triggered by theleading edge of an output pulse from the flip-flop 87, and whentriggered functions to sample the voltage appearing on electrical lead96 at that instant and to produce an output pulse having a magnitudeequal to that of the sampled voltage. The output of the sample and holdcircuitry 95 is fed through an electrical lead 98 to an output terminal99. The magnitude of the sampled ramp voltage appearing at tenninal 99is proportional to the phase difference initially applied to terminals51 and 52.

In operation, the electrical signals between which relative phasedifference is to be measured are fed to the input terminals 11 and 12,these signals being up-converted in the respective up-converters 20 and30. The phase measuring circuit 10 is directly adaptable for directionfinding use by merely connecting the device to an antenna array. In theembodiment of FIG. 1 a two-antenna array is shown, the antennas beingdesignated by the reference numerals 11011 and 012. The antenna 101 isconnected to the input terminal 111 of the phase-measuring circuit by anelectrical lead 103, the antenna 1102 being connected to the inputterminal 12 by an electrical lead 104. With any antenna orientationother than directly broadside an incoming signal wave front will impingeon one of the antennas before it arrives at the other antenna, therebygiving rise to a phase difference between the signals appearing at theinput terminals 111 and 112, this phase difference being indicative ofthe angle of arrival of the wave front.

The signals fed to the input terminals 111 and 112 are up-converted inthe respective (mixers) up-converters and 30. The signals injected intothe up-converters from the local oscillator 00 are given by:

E20: jw t E: jm l+w AllC Where,

E voltage applied to up-converter 20 through transmission line 4111 Evoltage applied to up'converter 30 through transmission line 412 w,angular frequency of VCO 40 A1 difference in effective line lengths oftransmission lines 41 and 12 C velocity of propagation in lines M and d2The difference in phase (A l at the up-converters (mixers) 20 and 30 isthen:

Now for example if Al/A 50 then a change of 1 percent in A, (or thefrequency of VCO 40) will cause a 180 change in the phase differencebetween the pump signals fed to the two mixers. This phase difference ispreserved in the mixing process and adds to the phase difference of theinput signals at terminals 111 and 112.

The up-converted signal outputs of the mixers 20 and 30 are applied tothe respective low-pass filters 22 and 32 so that only the differencefrequency outputs are fed to the phase detector 60. The leading edge ofthe output pulse from the summing amplifier 70, assuming that it is ofsufficient magnitude to pass through the threshold detector 70, triggersthe flip-flop 77, the output of the flip-flop 77 in turn triggering theramp generator 90 to initiate a ramp voltage output pulse. Thus, thevoltage ramp is synchronized to the leading edge of the summed signaloutput pulse of the phase detector.

The voltage ramp output of the ramp generator 90 is fed to the VCO 40 asthe control voltage therefor, frequency modulation of the VCO 40 withthis voltage ramp changing its output frequency in a linear manner,thereby causing an increasing phase shift difference in the up-convertedsignals due to the different effective line lengths which feed the pumpfrequency to the mixers 20 and 30. Thus, the difference frequency outputof the phase detector 60 (appearing at the output terminal 81) iscontinually changing due to the changing difference in phase between theup-converted signals fed to the phase detector. This changing differenceoutput is differentiated in order to determine the instant of phasereversal (zero crossover point) of the signals fed to the phasedetector. The output of the differentiator 84 provides positive andnegative pulses at the zero crossover points, the polarity of the pulsesdepending upon the direction of the relative phase reversals. Forexample, a positive going zero crossover might produce a positivedifferentiator output pulse, a negative going zero crossover thenproducing a negative differentiator output pulse.

The flip-flop 07 is of the type which is triggered only by positivepulses, hence will be triggered in the present circuit only bydifferentiator output pulses resulting from positive going zerocrossovers.

Thus, it is apparent that at some time after the voltage ramp isinitiated the phase detector output will indicate a change from aleading to a lagging phase relationship between the signals applied toits input terminals 011 and 02. At the instant of a positive going zerocrossover the flip-flop 07 is triggered and the sample and holdcircuitry then functions to measure the instantaneous value of the rampvoltage appearing on the electrical lead 96, and to hold this voltage(while the ramp voltage continues onto its maximum value), this voltagebeing proportional to the phase difference that initially existedbetween the applied input signals.

The antennas 1011 and 102 should be spaced apart be several wavelengthsif possible in order to increase accuracy of angle of arrivalmeasurements, to allow the use of broader band (and consequently larger)antennas without physical interference, and to avoid mutual couplingeffects. However, wide antenna spacing will result in ambiguous ormultivalued angle of arrival for a given phase difference. The ambiguitymay be resolved by making two simultaneous phase measurements betweencolinear (or at least parallel) pairs of antennas with differingseparations. The block diagram of a colinear interferometer system isshown in lFlIG. 2.

In the colinear interferometer system of FIG. 2 three antennas are used,the antennas being indicated by the reference numerals 1106, 1107 and100, the combination of the antennas 1106 and 1107 forming one pairseparated by a larger distance 5,, the antennas 107 and forming anotherpair separated by a smaller distance S The antenna 106 is connected toone input terminal of a hybrid junction 11110, the other input terminalbeing terminated in its characteristic impedance. The antenna 107 isconnected to one input terminal of a hybrid junction 1120, the otherinput terminal of the hybrid junction 1120 being terminated in itscharacteristic impedance. The antenna 100 is connected to one inputterminal of a hybrid junction 130, the other input terminal of thehybrid junction 130 being terminated in its characteristic impedance.

The colinear interferometer system of F IG. 2 utilizes two of the basicphase-measuring circuits 10 of FIG. 11, the two circuits being indicatedin H6. 2 by the reference numerals 110 and 110". One input terminalofthe phase-measuring circuit 10 is connected to an output terminal ofthe hybrid junction 1110 by an electrical lead 111, the other outputterminal of the hybrid junction 1110 being terminated in itscharacteristic impedance. The other input terminal of thephase-measuring circuit 110 is connected by an electrical lead 121 toone of the output terminals of the hybrid junction 1120, the otheroutput terminal of the hybrid junction 1120 being connected by anelectrical lead 122 to one of the input terminals of the phasemeasuringcircuit 10'. The other input terminal of the phasemeasuring circuit 110'is connected to one of the output terminals of the hybrid junction 1310by an electrical lead 131, the other output terminal of the hybridjunction 1130 being terminated in its characteristic impedance.

A received signal will impinge on the antennas 1106, 1107 and 1108 atdifferent times, the phase difference in impingement on the antennas1106 and 1107 producing an output at the output terminal 99 of thephase-measuring circuit 10 indicated by the notation Ad In a similarmanner, the difference in phase indicated by impingement of the signalon the antennas 1107 and 100 will produce an output signal indicated asA0, at the output terminal 99' of the phase-measuring circuit 10'. Byplotting A0 versus A0, for various angles of arrival, one can see thatknowing the frequency of the received signal and the two A05, the angleof arrival can be determined. P10. 5 of the drawing shows a plot of A0versus A49, for a typical example wherein the spacing S is 3.0)\ and theantenna 8,, is 2.4) at the high end of the band (5:4) with the pointscorresponding to physical angle of arrival indicated. Thus, for example,if A, was measured as plus 60 and Ad was measured at minus 95, then aphysical angle of arrival of minus 65 would be indicated.

In FIG. 6 of the drawing there is shown the schematic diagram ofpresently preferred transistorized circuitry for the ramp generator 90of FIG. 1. The circuit uses nine transistors,

indicated by the reference characters -0 The basic functions of thesetransistors are as follows: Transistor Q; as a blocking oscillator,transistor Q, being an output transistor to provide a signal indicativeof initiation of the ramp by operation of the blocking oscillatortransistor 0,. Transistor O and Q function as a switching circuittriggered by the blocking oscillator transistor 0,. Transistors Q and 0,function as amplifiers, transistor 0, functioning as a currentgenerator. Transistors Q, and Q, form a push-pull emitter-follower drivecircuit.

The ramp generator is provided with input terminal 91, to whichelectrical lead 78 of FIG. 1 is connected, and an output terminal 92, towhich are connected the electrical leads 93 and 96 of FIG. 1. Thevoltage ramp is initiated by a triggering voltage applied to inputterminal 91 from the phase detector 60 through electrical lead 78. Thistrigger trips the blocking oscillator consisting primarily of transistor0; and a blocking oscillator transfonner 151. The blocking oscillatoroutput pulse is coupled through transformer 151 to transistor Q whichacts to switch off transistor 0,, thereby allowing current generatortransistor Q, to charge a capacitor 152.

The ramp voltage generated across capacitor 152 is applied to the baseelectrode of transistor 0,, and is amplified by transistors Q and Q andthen fed to the push-pull emitterfollower drive circuit employingtransistors 0 and Q The output at terminal 92 is applied to the repellerelectrode of the Klystron tube forming VCO 40 by means of electricallead 93 to shift the frequency of the common pump oscillator.

The pulse generated by the blocking oscillator should preferably lastfor about V2 to V4 of a microsecond, after which the transistor 0, isagain turned on to allow quick return of the ramp by the push-pullemitter-following circuit to thereby provide the desired steep trailingedge to ready the circuit for the next trigger. Fast recovery is alsofacilitated by the use of direct coupling throughout the ramp generatorcircuitry, direct coupling also avoiding level shifts as a function ofthe repetition rate of the trigger signals which may be applied to theinput terminal 91. In this illustrative example, the nominal time forthe voltage ramp to reach its maximum value is 350 nanoseconds.

In FIG. 7 of the drawing there is shown the schematic diagram ofpresently preferred transistorized circuitry for the sample and holdcircuitry 95 of FIG. 1. The main functions of the circuit are performedby transistors O O 0, and 0, a flip-flop multivibrator 165, and adifferential amplifier 167. The circuit is provided with a pair of inputterminals 161 and 162, an output terminal 99 (as indicated in FIG. 1),and a slow ramp generator 170.

The electrical lead 96 from the ramp generator 90 is connected to theinput terminal 161 to provide for sampling of the voltage ramp byimpressing this voltage on the base electrode of transistor Q At thesame time an internal ramp voltage is generated by the action oftransistor Q and a capacitor 164, this internal ramp being initiated byactuation of the blocking oscillator in the ramp generator 90. thecollector electrode of transistor Q being coupled to the base electrodeof transistor O This internal ramp tends to be faster than the rampbeing sampled, but the transistor Q12 forces the internal ramp to slowdown and track the ramp applied to input terminal 161.

The input terminal 162 is connected to electrical lead 88 which feeds tothe sample and hold circuitry trigger pulses derived from differentiator84 output pulses resulting from positive going zero crossovers. Thetrigger pulses applied to input terminal 162 control operation offlip-flop 165. The output of flip-flop 165 is coupled to the emitterelectrode of transistor 0., through a series combination of asemiconductor diode 171 and a Zener diode voltage regulator 172, therectifier output of flip-flop 165 functioning to cut off transistor Q tothereby stop the ramp voltage across capacitor 164 and remove itsdischarge path, thereby holding the ramp at the level reached at theinstant of transistor Q cut off.

The output of transistor Q is taken from its collector electrode andapplied to one input of a comparator formed by transistors O and Q138-Also applied to this comparator is the output of slow ramp generator 170(the output of slow ramp generator 170 being a voltage ramp which risesat a slower rate than the output of ramp generator the comparator outputbeing applied to the inputs of difference amplifier 167. The differenceamplifier 167 functions to generate a gating signal output when the slowramp reaches the sampled and held voltage. This output voltage is fed tooutput tenninal 99 by electrical lead 98, it being presently preferredto utilize this output to stop an encoding counter.

Although in the illustrative example only the positive going zerocrossovers are used as triggers, it is also possible to utilize negativegoing zero crossovers together with the incorporation of circuitry toadd a voltage increment representing 180 to the sampled and held output.Furthermore, it might be desirable in some applications to provide fortriggering by both positive going and negative going zero crossovers.

In FIG. 3 of the drawing there is illustrated how two of the basicphase-measuring circuits 10 of FIG. 1 can be utilized in a frequencymeasuring system. As in FIG. 2, the two basic phase-measuring circuitsare indicated by the reference numerals 10 and 10. The signal whosefrequency is to be measured is fed to the input of a power divider 115.The power divider can be conveniently formed from an assembly of hybridmatrixes, for example. The power divider 115 is provided with two setsof output terminals, respectively indicated by the reference numerals 116 and 117, and 1 l8 and 1 19. The output terminals 1 16 and l 17 arecoupled to the two inputs of the phase-measuring circuit 10 by a pair oftransmission lines 124 and 125, these transmission lines being ofdifferent lengths. The power divider output terminals 118 and 119 arecoupled to the two inputs of the phase-measuring circuit 10 by a pair oftransmission lines 126 and 127, these lines being of different lengths.

In order to obtain the desired frequency sensitivity the line lengthdifferential between the transmission lines 124 and 125 must bedifferent that the line length differential between the transmissionlines 126 and 127. It is presently preferred, as a matter ofconvenience, to make the line length differential ratio correspond tothe antenna spacing ratio.

Thus, It is seen that frequency is detennined in the circuit of FIG. 3in much the same manner as angle of arrival is determined in the circuitof FIG. 2, simultaneous phase differences being measured by the basicphase-measuring circuits l0 and 10. The measured phase differences ofthe signals are proportional to the frequency of the signal applied tothe input of the power divider 1 15.

In FIG. 4 of the drawing there is shown how the basic phasemeasuringsystem of FIG. 1 can be modified to cover two separate frequency rangesand to yield increased sensitivity, the electrical leads 16 and 19 inthe FIG. 1 circuit being opened to permit insertion of additional RFcircuitry. 1n the drawing of FIG. 4 the broken parts of these lines areindicated as 16 and 16, and as 19 and 19', respectively. The lead 16 terminates in a terminal 216, the lead 19 terminating in a terminal 219.The upper ends of the leads 16' and 19' are provided with respectiveterminals 216' and 219. It is clear then that the basic circuit of FIG.1 would result if the terminals 16 and 16 were interconnected andterminals 19 and 19' interconnected.

The additional circuit elements added in the FIG. 4 circuit comprise anRF section including signal input terminals 211 and 212, a pair ofup-converter devices 220 and 230, and a voltage controlled oscillator240 to function as a common pump for the up-converters 220 and 230, theVCO output being fed to the up-converter 220 by a transmission line 241and to the up-converter 230 by a transmission line 242. the effectivelength of the transmission line 241 being longer than that of the line242.

A pair of antennas 201 and 202 are connected to the respective inputterminals 211 and 212 by leads 203 and 204,

the signals applied to the input terminal 211 and being fed to theupnconverter 220 by an electrical lead 221. Signals applied to the inputtenninal 212 are fed to the up-converter 230 by an electrical lead 231.

The output of up-converter 220 is fed through an electrical lead 221 toa low-pass filter 222, the output of up-converter 230 being fed throughan electrical lead 231 to a low-pass filter 232. The preceding describedRF section is intended for operation over the frequency range of from0.6-2.0 Gc. and with the VCO 240 operating at 12.5 Gc., whereby theup-converter outputs will be within the range of 8-12 Gc. as determinedby the difference frequency limits. Accordingly, the low-pass filters222 and 232 have a cutoff frequency slightly above 12 Gc.

The output of the low-pass filter 222 is fed to an input terminal 2511of a hybrid junction 250 through an electrical lead 256. The output ofthe low-pass filter 232 is fed to an input terminal 261 of a hybridjunction 260 through an electrical lead 266.

The hybrid junction 250 is provided with another input terminal 252 anda pair of output terminals 253 and 254. The hybrid junction 260 isprovided with another input terminal 262 and a pair of output terminals263 and 26d. The output terminal 253 of hybrid junction 250 is connectedto the input of a traveling wave tube amplifier 270, abbreviated TWT,the TWT output being connected to a terminal 275. The output terminal2541 of hybrid junction 250 is terminated in its characteristicimpedance. The output terminal 263 of hybrid junction 260 is connectedto the input of a TWT 280, the out-- put of TWT 280 being connected to aterminal 235. The output terminal is of hybrid junction 260 isterminated in its characteristic impedance.

The control voltage input of VCO 240 is connected by an electrical lead293 to the output of ramp generator 90, which then serves to provide thecontrol voltage for both of the VCOs 40 and it is apparent that byinterconnection of the terminal 216 to input terminal 252 of hybridjunction 250, terminal 219 to input terminal 262 of hybrid junction 260,terminal 275 to terminal 216', and terminal 285 to terminal 219', (theseinterconnections being omitted in the diagram of FIG. 41 in order tomore clearly depict the basic system of FIG. 1) the 0.6-2.0 Gc. RFsection will be added to the basic FIG. 1 circuit to extend the range ofthe basic circuit to include 0.6-2.0 Gc. as well as 2-6 Gc. Thus thefrequency range of the basic system can be extended even further with aminimum of additional components. As shown in the illustrative exampleof FIG. 4 the addition of TWTs is possible since the outputs of the RFsections are in the identical compressed frequency range. Those skilledin the art will appreciate that further extensions of the FIG. 41circuit concept will enable bandswitching of multiple RF sections toprovide a selection of different system frequency ranges. Hence,although the invention has been described with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that certain changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

What is claimed is:

ll. A system for measuring the relative phase difference between twoelectrical signals, one of the signals being applied to a first signalinput terminal and the other signal being simultaneously applied to asecond signal input terminal, said system comprising:

a. first and second up-converter devices, each having pump and signalinputs, the signal input of said first up-converter device being coupledto said first signal input terminal, the signal input of said secondup-converter device being coupled to said second signal input terminal;

. a variable frequency pump oscillator the frequency of which iscontrollable by an applied electrical signal; 0. first transmission linemeans coupling the output of said variable frequency pump oscillator tothe pump input of said first up-converter device;

d. second transmission line means coupling the output of said variablefrequency pump oscillator to the pump input of said second up-converterdevice, the effective line length of said second transmission line meansbeing different from that of said first transmission line means;

. signal-generating means coupled to the outputs of said first andsecond up-converter devices for generating a predetermined electricalsignal in response thereto, said signal-generating means also beingcoupled to said variable frequency pump oscillator to apply saidgenerated predetermined electrical signal thereto for altering thefrequency thereof to cause a continually increasing relative phase shiftof the signal outputs of said first and second up-converter devicesthrough a point of phase coincidence; and signal-sampling means coupledto said signal-generating means for deriving from said generatedpredetermined electrical signal at the instant of phase coincidence ofthe up-converted signals an output signal proportional to the phasedifference between the signals applied to said first and second signalinput terminals.

2. The phase measuring defined in claim 1, wherein the frequency of saidpump oscillator is controllable in accordance with the magnitude of theapplied electrical signal, wherein said generated predeterminedelectrical signal is a voltage ramp pulse, and wherein the magnitude ofsaid voltage ramp pulse at said instant of phase coincidence isproportional to the phase difference between the signals applied to saidfirst and second signal input terminals.

3. A system for measuring the relative phase difference between twoelectrical signals, one of the: signals being applied to a first signalinput terminal and the other signal being simultaneously applied to asecond signal input terminal, said system comprising:

a. a local frequency generator means, the frequency of which iscontrollable by an applied electrical signal;

b. first and second frequency converter devices, each being adapted toreceive oscillator signals and signal inputs, the signal input of saidfirst frequency converter device being coupled to the first signal inputterminal, the signal input of said second frequency converter devicebeing coupled to said second input terminal;

c. first transmission line means coupling the output of said frequencygenerator means to the pump input of said first frequency converterdevice;

d. second transmission line means coupling the output of said frequencygenerator means to the pump input of said second frequency converterdevice;

e. signal generator means coupled to the outputs of said first andsecond frequency converter devices for generating a predeterminedelectrical signal in response thereto, said signal generating means alsobeing coupled to said frequency generator means to apply said generatedpredetermined electrical signal thereto for altering the frequencythereof to cause a continually varying phase shift of the signal-outputof said first and second frequency converter devices through a point ofphase coincidence; and

f. signal sampling means coupled to said signal-generating means forderiving from said generated predetermined electrical signal at theinstant of phase coincidence of the frequency converted signals anoutput signal proportional to the phase difference between the signalsapplied to said first and second signal input terminals.

4. The phase-measuring system defined in claim 2. wherein saidsignal-generating means includes phase combining and detecting means forproducing a first electrical output having a magnitude proportional tothe sum of the phases of signals appearing at the outputs of said firstand second up-converter devices, and wherein said signal generatingmeans further includes voltage ramp pulse generator means for generatingsaid voltage ramp pulse whenever the first electrical output of saidphase combining and detecting means exceeds a predetermined thresholdvalue.

5. The phase-measuring system defined in claim 4, wherein said phasecombining and detecting means also includes means for producing a secondelectrical output having a magnitude proportional to the differencebetween the phases of signals appearing at the outputs of said first andsecond upconverter devices, said second electrical output therebyundergoing a reversal of polarity at said instant of phase coincidence,said second electrical output being coupled to said signal samplingmeans, and wherein said signal sampling means presents an outputrepresentative of the magnitude of said voltage ramp pulse at theinstant of polarity reversal of the second electrical output of saidphase combining and detecting means.

6. The phase-measuring system defined in claim 5, wherein saidsignal-sampling means includes difierentiating means coupled to thesecond electrical output of said phase combining and detecting means,said difierentiating means producing a pulse whenever said secondelectrical output undergoes a polarity reversal, the polarity of thepulsed produced by said differentiating means depending upon thedirection of polarity reversals of said second electrical output; saidsignal sampling means further including triggering means coupled to theoutput of said differentiating means for producing a trigger pulse onlyupon occurrence of differentiating means output pulses of apredetermined polarity, and wherein said signal-sampling means presentsan output only upon occurrence of said trigger pulses.

7. The phase-measuring system defined in claim 5, wherein said phasecombining and detecting means includes a hybrid junction having a firstinput tenninal coupled to the output of said first up-converter deviceand a second input terminal coupled to the output of said secondup-converter device and first and second output terminals, summingamplifier means, difference amplifier means, and first and second signalenvelope detector means, said first signal envelope detector meanscoupling the first output terminal of said hybrid junction to one inputterminal of each of said summing amplifier means and said differenceamplifier means, said second signal envelope detector means coupling thesecond output terminal of said hybrid junction to the other inputterminal of each of said summing amplifier means and said difierenceamplifier means.

8. The phase-measuring system defined in claim 6, wherein saidsignal-sampling means further includes sample and hold means coupled tothe output of said voltage ramp pulse generator and to the output ofsaid triggering means for generating a sampling voltage the magnitude ofwhich has the same instantaneous value as that of said voltage ramppulse until occurrence of said trigger pulse at which time the samplingvoltage is then held constant.

9. The phase-measuring system defined in claim 2, wherein said first andsecond up-converter devices are microwave mix ers having upper and lowersideband outputs, wherein said first transmission line means isconnected to the pump input of said first up-converter device by meansfor filtering out a predetermined one of said sideband outputs, andwherein said second transmission line means is connected to the pumpinput of said second up-converter device by means for filtering out saidpredetermined one of said sideband outputs.

10. The phase-measuring system defined in claim 4, wherein saidsignal-generating means includes detector means coupled to the firstoutput of said phase combining and detecting means for producing anelectrical output only when the first electrical output of said phasecombining and detecting means exceeds said predetermined thresholdvalue, and triggering means coupling the output of said detecting meansto said voltage ramp pulse generator means to control actuation thereof.

1. A system for measuring the relative phase difference between twoelectrical signals, one of the signals being applied to a first signalinput terminal and the other signal being simultaneously applied to asecond signal input terminal, said system comprising: a. first andsecond up-converter devices, each having pump and signal inputs, thesignal input of said first up-converter device being coupled to saidfirst signal input terminal, the signal input of said secondup-converter device being coupled to said second signal input terminal;b. a variable frequency pump oscillator the frequency of which iscontrollable by an applied electrical signal; c. first transmission linemeans coupling the output of said variable frequency pump oscillator tothe pump input of said first up-converter device; d. second transmissionline means coupling the output of said variable frequency pumposcillator to the pump input of said second up-converter device, theeffective line length of said second transmission line means beingdifferent from that of said first transmission line means; e.signal-generating means coupled to the outputs of said first and seconDup-converter devices for generating a predetermined electrical signal inresponse thereto, said signal-generating means also being coupled tosaid variable frequency pump oscillator to apply said generatedpredetermined electrical signal thereto for altering the frequencythereof to cause a continually increasing relative phase shift of thesignal outputs of said first and second up-converter devices through apoint of phase coincidence; and f, signal-sampling means coupled to saidsignal-generating means for deriving from said generated predeterminedelectrical signal at the instant of phase coincidence of theup-converted signals an output signal proportional to the phasedifference between the signals applied to said first and second signalinput terminals.
 2. The phase measuring defined in claim 1, wherein thefrequency of said pump oscillator is controllable in accordance with themagnitude of the applied electrical signal, wherein said generatedpredetermined electrical signal is a voltage ramp pulse, and wherein themagnitude of said voltage ramp pulse at said instant of phasecoincidence is proportional to the phase difference between the signalsapplied to said first and second signal input terminals.
 3. A system formeasuring the relative phase difference between two electrical signals,one of the signals being applied to a first signal input terminal andthe other signal being simultaneously applied to a second signal inputterminal, said system comprising: a. a local frequency generator means,the frequency of which is controllable by an applied electrical signal;b. first and second frequency converter devices, each being adapted toreceive oscillator signals and signal inputs, the signal input of saidfirst frequency converter device being coupled to the first signal inputterminal, the signal input of said second frequency converter devicebeing coupled to said second input terminal; c. first transmission linemeans coupling the output of said frequency generator means to the pumpinput of said first frequency converter device; d. second transmissionline means coupling the output of said frequency generator means to thepump input of said second frequency converter device; e. signalgenerator means coupled to the outputs of said first and secondfrequency converter devices for generating a predetermined electricalsignal in response thereto, said signal generating means also beingcoupled to said frequency generator means to apply said generatedpredetermined electrical signal thereto for altering the frequencythereof to cause a continually varying phase shift of the signal outputof said first and second frequency converter devices through a point ofphase coincidence; and f. signal sampling means coupled to saidsignal-generating means for deriving from said generated predeterminedelectrical signal at the instant of phase coincidence of the frequencyconverted signals an output signal proportional to the phase differencebetween the signals applied to said first and second signal inputterminals.
 4. The phase-measuring system defined in claim 2, whereinsaid signal-generating means includes phase combining and detectingmeans for producing a first electrical output having a magnitudeproportional to the sum of the phases of signals appearing at theoutputs of said first and second up-converter devices, and wherein saidsignal generating means further includes voltage ramp pulse generatormeans for generating said voltage ramp pulse whenever the firstelectrical output of said phase combining and detecting means exceeds apredetermined threshold value.
 5. The phase-measuring system defined inclaim 4, wherein said phase combining and detecting means also includesmeans for producing a second electrical output having a magnitudeproportional to the difference between the phases of signals appearingat the outputs of said first and second up-converter devices, saidsecond electrical output thereby underGoing a reversal of polarity atsaid instant of phase coincidence, said second electrical output beingcoupled to said signal sampling means, and wherein said signal samplingmeans presents an output representative of the magnitude of said voltageramp pulse at the instant of polarity reversal of the second electricaloutput of said phase combining and detecting means.
 6. Thephase-measuring system defined in claim 5, wherein said signal-samplingmeans includes differentiating means coupled to the second electricaloutput of said phase combining and detecting means, said differentiatingmeans producing a pulse whenever said second electrical output undergoesa polarity reversal, the polarity of the pulsed produced by saiddifferentiating means depending upon the direction of polarity reversalsof said second electrical output; said signal sampling means furtherincluding triggering means coupled to the output of said differentiatingmeans for producing a trigger pulse only upon occurrence ofdifferentiating means output pulses of a predetermined polarity, andwherein said signal-sampling means presents an output only uponoccurrence of said trigger pulses.
 7. The phase-measuring system definedin claim 5, wherein said phase combining and detecting means includes ahybrid junction having a first input terminal coupled to the output ofsaid first up-converter device and a second input terminal coupled tothe output of said second up-converter device and first and secondoutput terminals, summing amplifier means, difference amplifier means,and first and second signal envelope detector means, said first signalenvelope detector means coupling the first output terminal of saidhybrid junction to one input terminal of each of said summing amplifiermeans and said difference amplifier means, said second signal envelopedetector means coupling the second output terminal of said hybridjunction to the other input terminal of each of said summing amplifiermeans and said difference amplifier means.
 8. The phase-measuring systemdefined in claim 6, wherein said signal-sampling means further includessample and hold means coupled to the output of said voltage ramp pulsegenerator and to the output of said triggering means for generating asampling voltage the magnitude of which has the same instantaneous valueas that of said voltage ramp pulse until occurrence of said triggerpulse at which time the sampling voltage is then held constant.
 9. Thephase-measuring system defined in claim 2, wherein said first and secondup-converter devices are microwave mixers having upper and lowersideband outputs, wherein said first transmission line means isconnected to the pump input of said first up-converter device by meansfor filtering out a predetermined one of said sideband outputs, andwherein said second transmission line means is connected to the pumpinput of said second up-converter device by means for filtering out saidpredetermined one of said sideband outputs.
 10. The phase-measuringsystem defined in claim 4, wherein said signal-generating means includesdetector means coupled to the first output of said phase combining anddetecting means for producing an electrical output only when the firstelectrical output of said phase combining and detecting means exceedssaid predetermined threshold value, and triggering means coupling theoutput of said detecting means to said voltage ramp pulse generatormeans to control actuation thereof.